EDIT

source data of media entities need to be added to the IIIF manifests.

This need to be implemented into the ManifestComposer

source information can be added to the iiif manifest as metadata as exemplified in https://iiif.io/api/presentation/3.0/#b-example-manifest-response

"metadata": [
    {
      "label": { "en": [ "Source" ] },
      "value": { "none": [ "<span>From: <a href=\"https://example.org/db/1.html\">Some Collection</a></span>" ] }
    }
]